The U.S. Navy AEGIS (AN/SPY-1) system makes uses of sophisticated (SPY-1D) phased array radar sensors and powerful AN/UYK-43/44 computers to track airborne, surface, and submerged targets. Upon release from the AEGIS controller, the system can control other ships sensor and weapons systems, and in fact can release its own as well as other ship's weapons to bear upon attacking aircraft or missiles.
The AEGIS system antenna, the SPY-1D phase array radar antenna, are capable of being electronically steered without mechanical movement. Thus the SPY 1A antenna consist of phase elements on all four sides of the ship's upper super-structure.
The system includes a fire control, tactical display, and operators consoles that allow for visualization of the entire battle environment. Friendly and Aggressor airframes can be tracked by the system using IFF (identification-friend or foe) systems. However, civilian aircraft not sporting the military ID systems are at risk in combat zones since only operator interpretation of flight performance and positioning will make the determination of a civilian aircraft. As in the case of the U.S.S. Vincennes patrolling the Persian Gulf, a civilian aircraft which appears to be oncoming and losing altitude may be interpreted as making a hostile run at a battle group and will be fired upon to protect the combat vessels. While radio contact is attempted, it is up to the Captain and the Battle Group Commander to determine if the risk to ships under authority are worth mis-identification of a possible hostile aircraft.
Upgrades to the system are ongoing, with better radar signature information allowing for more precise location and tracking information as well as countering electronic counter-measures which could jam radar.
A key component of the AEGIS system is the ability to integrate various other detection and tracking signals from other aircraft and surface vessels. This includes data from naval helicopters providing over the horizon tactical data on surface and airborne contacts. This also includes possible data input from TR-1 (tactical data version of the U-2) providing recon data from high above the AEGIS cruiser.
Since the AEGIS antenna structure is so large and must allow antenna elements facing in each of four quadrants, the AEGIS ship is a purpose built vessel. Originally embarked in the Ticonderoga (CG-47) class cruiser, the Arleigh Burke (DDG-51) class of destroyer also introduced the AEGIS system to the smaller vessels.
During the Gulf War, AEGIS equipped ships fired numerous Tomahawk TLAM (Tactical Land Attack cruise Missile) deep into Iraq from firing positions in the Gulf. Various post Gulf War strikes on Iraq have also involved AEGIS ships.
The first demonstration system for AEGIS was put to see in 1973 embarked upon the USS Norton Sound (AVM 1).